1. Field of the Invention
The present invention relates to a mobile communication system and, more particularly, to a mobile communication system which restricts the use of mobile station radio units (to be referred to as mobile units hereinafter), which are used for mobile communication, in places where troubles may be caused by radio waves radiated from the mobile units or in places where speech communication through the mobile units makes the people around the mobile units uncomfortable.
2. Description of the Prior Art
Mobile communication is information communication performed by radio. Portable mobile units represented by portable telephones, pagers, and the like have recently become widespread because they allow communication at any time and in any place or during movement.
FIG. 1 is a block diagram showing the schematic arrangement of a conventional portable telephone 20.
The portable telephone 20 includes a transmission/reception antenna 21 for receiving a data signal from a base station and transmitting a data signal to the base station, a reception circuit 22 for amplifying the data signal received through the transmission/reception antenna 21, a demodulation circuit 23 for regenerating a clock by regenerating a baseband signal from the data signal amplified by the reception circuit 22, a speech decoding circuit 24 for converting the regenerated baseband signal into an analog speech signal and outputting it from a speaker 31, a speech encoding circuit 26 for converting an analog speech signal input from a microphone 32 into a baseband signal, a modulation circuit 27 for modulating the baseband signal into a transmission data signal in accordance with a certain modulation method, a transmission circuit 28 for amplifying the transmission data signal, a timing control circuit 25 for controlling the overall timing of the portable telephone 20, and a CPU 29 for controlling the overall operation of the portable telephone 20.
The operation of the portable telephone 20 will be described next.
When the power supply (not shown) for the portable telephone 20 is turned on, all the circuits are activated, a position registration signal for registering the position of the portable telephone 20 in the base station is transmitted from the transmission/reception antenna 21 to the base station through the modulation circuit 27 and the transmission circuit 28 under the control of the CPU 29. The portable telephone 20 is then set in the wait state. In the wait state, the operation mode of the portable telephone 20 is switched to the intermittent reception mode in which the supply of clocks from the timing control circuit 25 is, minimized, and the power supply for the reception circuit 22 and the demodulation circuit 23 is turned on only in time slots required for the reception of information from the base station. The speech decoding circuit 24, the speech encoding circuit 26, the modulation circuit 27, and the transmission circuit 28 are set in the standby state. In the intermittent reception mode, intermittent reception is performed several times in several hundred ms (milliseconds). When a terminating or originating operation is to be performed, the operation mode is switched to the speech communication mode.
In the speech communication mode, a data signal received from the base station through the transmission/reception antenna 21 is output as speech data from the speaker 31 through the reception circuit 22, the demodulation circuit 23, and the speech decoding circuit 24. Speech data input from the microphone 32 is converted into a data signal through the speech encoding circuit 26, the modulation circuit 27, and the transmission circuit 28 and is transmitted from the transmission/reception antenna 21 to the base station.
In the conventional mobile communication system, therefore, as long as the power supply for the mobile unit is turned on in a service area, communication can be performed in any place, i.e., a place where troubles may be caused by radio waves and a place where speech communication makes the people around the mobile unit uncomfortable.
It is said that radio waves radiated from mobile units such as portable telephones cause malfunctions in medical equipment, various types of instruments, and the like in hospitals, air planes, and the like. If, therefore, a user who knows nothing about this or a user who knows this information but forgets this enters a hospital or an air plane without turning off the power supply for the mobile unit, medical equipment, various types of instruments, and the like may malfunction.
In addition, since a mobile unit allows communication in public facilities, trains, and the like, communication sometimes makes the people around the mobile unit uncomfortable.
A system for forcibly making a mobile unit incapable of performing communication in places where the user of the use of the mobile unit needs to be inhibited, e.g., in trains, is disclosed in Japanese Unexamined Patent Publication No. 7-245782. According to the mobile communication system disclosed in Japanese Unexamined Patent Publication No. 7-245782, in places where the use of mobile units needs to be inhibited, the communication mode is switched to the pager mode to make the mobile unit incapable of performing communication, and at the same time, a terminating operation can be performed without making the people around the mobile unit uncomfortable. This system can only prevent speech communication from making the people around the mobile unit uncomfortable. This reference, however, gives no indication as to the problems caused by radio waves radiated from mobile units. This conventional system cannot prevent troubles caused by radio waves radiated from mobile units.